I apologize, but it's not possible to add more than one supplier to an inventory. A product can have several suppliers, one per inventory.
What's the correct way for adding a new inventory for a product variation, currently when we add a new one and save changes it doesn't save, and we find on the default main inventory, what could be go wrong?
As I read, you have enable the option of making all products MI. The correct way for adding inventories in a variation is exactly the same as in simple products, but within each variation. I've tested it in my local site and for me are saved all the inventories created. So please, as I couldn't reproduce it, I have to ask you to try this before keeping investigating:
- Make sure that you have the last update of your ATUM add-ons.
- If you have and the problem persists, try to deactivate all plugins except the ATUM add-ons and Woocommerce and check again.
Please, let me know what happens in order to keep investigating if we need to.
Is there a way to import the multiple locations for the inventory from Shopify export?
You should could do it, but you will need to do a middle step in order to adapt the info, there is no any 'direct' import.